Subscribe to our newsletter

How likely am I to get side effects from the morning after pill?

The morning after pill is a type of emergency contraception, used after unprotected sex to prevent pregnancy. There are two main kinds of contraceptive pill, one that goes under the brand name Levonelle, and one called ellaOne. The other form of emergency contraception sometimes used is the IUD or copper coil, which can be inserted up to five days after sex has taken place to prevent pregnancy.

Levonelle has been used as a form of emergency contraception for many years. The active ingredient is levonorgestrel, a synthetic (man-made) version of progesterone. Although we don’t know exactly how it works, its main action is thought to prevent or delay ovulation (the release of the egg), and thus prevent the egg getting fertilised.

It is believed that the levonorgestrel tricks the body into thinking that ovulation has already occurred, which prevents the release of the egg. Levonorgestrel also causes an increase in the thickness of mucus in the cervix, forming a barrier to make it difficult for sperm to enter the womb.

There are many generic versions of the same pill available, which contain the same amount and type of levonorgestrel, so don’t be alarmed if the morning after pill you are given isn’t called Levonelle.

ellaOne is a newer form of emergency contraceptive pill that is thought to be more effective than Levonelle in certain situations. For example, when taken more than 48 hours after intercourse has taken place, ellaOne is more likely to prevent pregnancy than Levonelle. If taken within 48 hours of intercourse, there is little difference between the two.1

The active ingredient in ellaOne is called ulipristal acetate. It works by altering the activity of naturally occurring progesterone by acting on the body’s progesterone receptors. Again, it effectively tricks the body into believing that ovulation has already occurred, resulting in ovulation being delayed or completely prevented.

Which side effects could affect me if I use the morning after pill?

All medications can cause side effects in some people, and the morning after pill is no exception. Not everyone that uses emergency contraception will experience side effects and it is pretty hard to predict who might get some and who won’t get any at all.

While no study has looked at which people are more likely to develop side effects, for women that do develop side effects they are usually quite mild, and resolve pretty quickly.There are a few more serious side effects that can occur, but these are rare.

It is also important to remember that the aim of taking emergency contraception is to prevent pregnancy, so many women are happy to experience certain mild side effects to ensure they prevent a pregnancy.

Below, we’ve looked at some of the side effects in more detail to determine how common they are, and what you can do to minimise them.

Feeling sick or having abdominal discomfort

Nausea (feeling sick) is pretty common if you take the morning after pill. It affects in over 10% of women who take it, and for every 10 women that do experience nausea, one of them will actually be sick (one woman in every 100 that take the pill).2 If you are sick within three hours of taking ellaOne or Levonelle, you need to take a second dose to ensure that it will still be effective.3

Simple things you can do to help reduce nausea are to take the morning after pill with food, eat regular snacks, and if you are feeling sick you could try over the counter anti-sickness medication on the advice of your pharmacist. If you have used the morning after pill previously and know it makes you feel sick, you can try taking anti sickness medication an hour before taking it.

It is also quite common after taking the morning after pill to develop mild stomach cramps – about 1 in 10 women are affected,4 but they usually settle relatively quickly. Often, women find painkillers such as ibuprofen or paracetamol helpful.

Tiredness and/or headache

After using hormonal emergency contraception, up to 1 in 10 women may develop symptoms of tiredness or headache. The main reason for this is the large dose of progesterone that the morning after pill contains, up to 50 times more than your body naturally produces to menstruate.5

For this reason, it is no surprise that symptoms similar to premenstrual syndrome (PMS) can develop. These include sore, tender breasts, tiredness, bloating, and headache.6

Changes in bleeding or irregular bleeding

Again, due to the large amount of progesterone, this can make your period heavier or lighter than normal, or it can make your period come at a different time of the month than you were expecting.7

Up to 1 in 10 women may notice some spotting before their period occurs, due, again, to the relatively high dose of progesterone. If the morning after pill is taken before ovulation occurs, it is likely to bring your period forward slightly.8

If the morning after pill is taken after ovulation has occurred, it usually results in a delay in your period, usually by a few days. It is completely normal for your period to be a few days late after using hormonal contraception. Up to 1 in 100 women who use emergency hormonal contraception experience a delay in the start of their period by seven days or more.9

Understandably this can cause anxiety, but if your period is more than five days late, then taking a pregnancy test is advised. If you develop pain or any other symptoms, it is important to see a doctor urgently to rule out an ectopic pregnancy, which can be dangerous.10

Diarrhoea, heartburn, or a dry mouth

These side effects can affect up to 1 in every 100 women who use hormonal emergency contraception.11 Again, these are thought to be symptoms similar to PMS, due to the high dose of progesterone. Women may also, or alternatively, suffer from hot flushes, anxiety, or trouble sleeping. Usually these symptoms resolve pretty quickly.

Very rare side effects

These occur in less than 1 in every 10,000 women who take the morning after pill, so it is very unlikely that you will experience these if you do need to use the morning after pill. Very occasionally, women may experience symptoms such as a rash, hives (an allergic reaction rash), or itching and swelling of the face. If these symptoms do occur, it is important to seek medical attention immediately.12

Who should not use the morning after pill?

For most women, the morning after pill is a safe and effective method of emergency contraception. However, there are some situations in which it should definitely not be used. If these situations affect you, it is important to seek help from your GP or local family planning clinic quickly for assessment for use of the copper coil.

ellaOne is not advised in women who have severe asthma (which is being treated by oral steroids) because it can have an antagonistic effect at the glucocorticoid receptors. This means that Ella One can stop the steroids from working quite as well. IellaOne should also not be used at the same time as Levonelle or any other morning after pill containing levonorgestrel), as this can make both morning after pills you take less effective.13

It is not advisable to use Levonelle or other levonorgestrel emergency contraception more than once in each menstrual cycle. If ovulation has been delayed (and not inhibited) and you use levonelle again, theoretically it may not delay ovulation again.

Levonelle is also not recommended in women at risk of ectopic pregnancy (for example women who have had previous salpingitis, or an infection). This is because although in theory it should stop or delay ovulation occurring, there is still a risk it will not, and could result in an ectopic pregnancy. The absolute risk of ectopic pregnancy is still likely to be low because Levonelle works mainly by stopping ovulation, and therefore fertilisation, from taking place. However, there is a possible risk.14

Both types of morning after pill are not recommended for women who have severe problems with liver function, certain bowel conditions such as Crohn’s disease (which can affect absorption of the pill), or individuals who are taking a group of medications called CYP3A4 inducers (found in anti-epileptic drugs and St John’s Wort). For most other women, it is safe and effective, however.15

If you are concerned that emergency contraception may not work, or is not safe for you because you are in one of the above groups, please discuss this with your pharmacist or doctor.

Featured image shows a pharmacist handing over a pill packet to a woman wearing a yellow jumper. The image is cropped so you can only see their hands, torsos, and the pharmacy counter.

Jennifer is a General Practitioner, medical writer, parent, and founder of the Grace Kelly Ladybird Trust, registered charity for childhood cancer awareness and research (www.gracekellyladybird.co.uk). She also has a particular interest in women’s and children’s health, and enjoys medical writing, particularly helping make medical information easily accessible to those who want to find out more.